An X-ray collimator limits and shapes the radiation field. In general radiography it commonly uses adjustable lead shutters and a light-field system to indicate the intended field. In CT and fluoroscopy, collimation may use different mechanics and control strategies, but the central purpose remains controlling beam geometry.

Key takeaways

  • Collimation reduces irradiation outside the intended field and helps control scatter.
  • A collimator may include shutters, motors, sensors, filtration, lamps or LEDs, optics, and controls.
  • Mechanical fit alone does not establish alignment, calibration, or system compatibility.

01

Beam limitation and field indication

Opposing shutters create a rectangular or otherwise defined field. A lamp or LED and mirror can project a visible light field that corresponds to the X-ray field in systems designed for light-field alignment. Scale indicators, field-size displays, or automatic collimation may help the operator set the field for the receptor geometry.

02

What is in the assembly?

Depending on design, a collimator can include multiple shutter stages, motors, belts or gears, encoders, position sensors, filters, a mirror, light source, thermal protection, local controls, and a communication interface. Some systems track source-to-image distance or receptor size and coordinate field limits automatically.

03

Why alignment matters

The indicated and actual radiation fields must correspond within applicable criteria, and the central ray must align with the imaging geometry. Mounting position, focal-spot location, mirror position, shutter position, calibration, and mechanical play can affect correspondence. A replacement generally requires specified alignment and performance verification.

04

Common symptom boundaries

A field that will not open or close can involve a motor, obstruction, belt, sensor, control board, power, communication, or safety state. A dim light field may involve the source, optics, power, contamination, or alignment. Separating mechanical, electrical, control, and calibration evidence prevents an unnecessary assembly replacement.

Safety boundary

Collimator testing can involve ionizing radiation. Field-alignment and output-related checks must be performed by qualified personnel using approved methods and calibrated instruments.

Related terminology

Terms with a published definition link directly to the glossary.

collimatorlight fieldradiation fieldfiltrationcentral ray